Tubular magnetic devices are used in many applications for influencing the travel of a charged particle. Permanent magnetic structures have many advantages over large solenoids and bulky power supplies in creating a magnetic field. Permanent magnet tubular devices have been used to create magnetic fields in such applications as traveling wave tubes, klystrons, wigglers, and twisters. An example of the use of a permanent magnet structure for producing a magnetic field in a hollow cylinder is disclosed in U.S. Pat. No. 4,994,778 entitled "Adjustable Twister" issuing to Herbert A. Leupold, the present inventor, on Feb. 19, 1991.
In many applications, such as those in medicine and in particular magnetic resonance imaging techniques, there is an ever increasing need for permanent magnet structures having specialized magnetic fields. While the prior art magnetic structures have provided magnetic fields suitable for their intended purpose, there is a need for other types of magnetic fields that are not readily achievable with known permanent magnet structures.